This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to JP2001-139449 filed in Japan on May 10 2001; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a lightweight wave gear drive equipped with a lightweight wave generator.
2. Description of the Prior Art
Reduction gears used in mechanisms for driving robots and the like include a wave gear drive that is manufactured and sold by the present inventors under the proprietary name xe2x80x9charmonic drive.xe2x80x9d A typical wave gear drive comprises a rigid, circular internal gear, a flexible, circular external gear disposed within the internal gear, and a wave generator. The wave generator comprises a rigid, elliptical wave-plug and a wave bearing on the outer periphery of the wave-plug. Thereby, the flexible external gear is flexed into an elliptical shape, causing the toothed portions of the flexible external gear at each end of the elliptical major-axis to mesh with the corresponding teeth of the rigid internal gear. When the wave generator is rotated by a motor, the positions at which the two gears mesh move around the circumference, generating a relative rotation arising from the difference in the number of teeth. Generally, the difference in the number of teeth in the two gears is two; with the internal gear being attached to a drive housing, the rotational output from the motor is taken off the external gear, with the rotational speed being greatly reduced by the difference in the number of teeth.
The present inventors have proposed reducing the weight of the wave gear drive thus configured by manufacturing the rigid internal gear and wave generator of a lightweight metal such as aluminum alloy. This is disclosed in, for example, JP-A Hei-10-318338.
When aluminum alloy is used to manufacture the wave gear drive to reduce the weight of the drive, aluminum alloy has good heat dissipation properties, so there is no problem in that regard. However, although titanium alloy is harder and stronger than aluminum alloy, it is not practical to manufacture a wave gear drive using titanium alloy because of its poor heat dissipation properties. Because the wave generator, in particular, is rotated at a high speed by the motor, the frictional contact portions of the wave bearing and the frictional contact portions between the wave generator and the external gear form the biggest source of heat in the wave gear drive. Therefore, if the hub and rigid cam-plate constituting the wave-plug of the wave generator are made of titanium alloy, they overheat and seize up.
An object of the present invention is to provide a wave gear drive having good heat dissipation properties that is provided with a wave generator formed of titanium alloy.
To attain the above and other objects, the present invention provides a lightweight wave gear drive comprising a rigid, circular internal gear, a flexible, circular external gear, and a wave generator that radially flexes the external gear into partial engagement with the internal gear and moves the position of engagement of the two gears in a circumferential direction, the wave generator including a circular hub, a rigid cam plate formed around an outer periphery of the hub, and a wave bearing provided between an outer peripheral surface of the rigid cam plate and an inner peripheral surface of the external gear, wherein, of the hub and the rigid cam plate, at least the rigid cam plate is formed of titanium alloy, and at least a portion of two sides of the rigid cam plate is formed as a crenellated heat-dissipating surface.
The wave generator, namely its rigid cam plate is the input element that is rotated at a high speed, so heat-dissipation can be improved by forming this portion as a crenellated heat-dissipating surface.
The heat-dissipating surface can be comprised by forming radial heat-dissipating fins. Also the hub and the rigid cam plate can be formed of titanium alloy as a single component.
It is desirable to plate the rigid cam plate surface with a heat-dissipating coating of a material such as copper having a higher coefficient of thermal conductivity than titanium alloy. Plating the surface of the titanium alloy, which does not have good thermal conductivity, with a metal having good thermal conductivity helps to increase the thermal diffusion and thus improve the rate at which heat is dissipated by contact parts.
The surface plating can have a thickness within the range of from five to fifty micrometers.
It is desirable to subject the surface of the rigid cam plate that is to be plated to surface hardening by shot peening. This makes it possible to increase the surface area of the rigid cam plate, thereby promoting heat dissipation.
In the lightweight wave gear drive of this invention, a heat-dissipating surface is formed on the rigid cam plate of the wave generator, which is the biggest source of heat. The wave generator rotates at high speed, so increasing the efficiency with which heat is radiated by this part makes it possible to prevent overheating. It is preferable to further enhance the heat dissipation properties by plating the part with a material such as copper having good heat-dissipating properties.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and following detailed description of the invention.